Ivab bennekfelt



[- RENNERFELT.

ELECTRIC FURNACE.

APPLICATION FILED OCT. 3. 1918.

1,305,167. Patented May27,1919,

In ve nfoh Q Ivar Rennerfelt IVAR RENNERFELT, OF DJURSHOLM, SXVEDEN.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented May 27, 1919.

Application filed October 3. 1913. Serial No. 256,651.

; m-ent in Electric Furnaces, of which the fol-' lowing is a specification.

This invention relates to improvements in electric furnaces.

Heretofore it has been known to heat objects in a furnace by means of centrally located vertical electrodes which generate arcs in contact with a furnace bottom adapted to rotate and provided with a contact bed 0 carbon of a suitable kind.

Such furnaces are, however, impractical, since the electrodes are apt to break OR if made to enter the rotating bed, especially if the bed is to be used as a heating resistance.

Furthermore it is impossible in furnaces of this type to connect the electrodes alternately in delta and star connection, which clearly is desirable in order to facilitate the control of the energy consumed by the furnace.

It has also beenheretofore known to heat an object centrally located in a furnace room, for instance a crucible, by means of two electric arcs, burning between two pairs 'of horizontal electrodes and heating opposite sides of the crucible. This way of heating offers. however, several disadvantages. Not only it impossible to uniformly heat a comparatively high object by means of horizontal arcs but it also is difficult to run a furnace of this kind with power from a supply circuit sensitive to fluctuations in the consumption of energy. This is the caseespecially at the period of starting when the furnace is cold.

This type of furnace is, furthermore, not well adapted to be run by means of polyphuse current in view of the fact that no less than six electrodes are required which occupy conside'able horizontal floor space. The arrangement of the electrodes also makes it difficult to equip the furnace with a sufficiently large charging door in the sidewall thereof.

It is possible to avoid the disadvantages enumerated above and to build a very useful and suitable furnace, if, jas is contemplated by the present invention, a plurality of electrodes are arranged iinthe furnace chamber near the sidewalls thereof so as to leave a free space in the center strongly heated and adapted to be used for melting or otherwise heating a charge in saidspace between the electrodes.

For certain purposes, especially when melting high grade glass for lamps, lenses, etc., one or more crucibles may preferably be placed directly on the bottom of said open space, facilitating a rapid melting and removal when necessary.

A prominent feature of the present invention resides in the use of crushed carbon, coke, graphite or any other suitable mate rial, which is preferably located on supports which extend from the bottom and sides of "the heating chamber of the furnace in such wise as to provide contacts for the arcs ofthe electrodes. These supports or extensions are built of highly refractory material for instance magnesite bricks or bricks ofcarbon or graphite. The sidewall of the furnace immediately behind each arc should also be protected against the exceedingly strong heat by means-of very refractory materials.

The contacts provided around the sidewall of the furnace may be connected either directly to each other using star connection or to the supply circuit. The arcs in this way are connected in delta causing the voltage of the arcs to increase by 73%. Conductors of for instance carbon are used forleading the current through the sidewalls.

Both direct and alternating current may be used. The frequency and number of phases is of no importance. The energy required is divided on a plurality of electrodes. their number depending on the number of phases and on the strength of current allowable on each electrode of a certain dimension. The number of electrodes is also easier in a furnace constructed in accordance with the present invention than in furnaces of other types. The reason for this is that the heat is radiated inward not only from the arcs themselves but also from the Walls by reverberation.

The means for introducing energy into the furnace are furthermore very simple and Figures 1 and 2 are vertical and horizontal sectional views,'respectively, of a furnace constructed for heatinga plurality of cru cibles, and Fig. 3 is a horizontal sectional view of a furnace constructed for heating only one crucible, said crucible being heated by means of a plurality of electrodes. -Any kind of current may be used in operating either furnace.

The electrodes 1 may be vertical or introduced in an inclined position through the or more crucibles 4 are placed in the center of the furnace for melting glass or other substances. By arranging the bottom of-the furnace as a melting hearth crucibles may be dispensed with.

Extensions 5 project from the sidewall,

carrying a'suitable contact material 6 for instance of coke or graphite more or less finely crushed and preferably supported by a layer 7 of bricks or plates of carbon or graphite. In order to protect the wall 3 against the intense heat given off by the heating arcs 8 it is preferred to place highly refractory plates 9 around said wall immediately behind the electrodes. At this place openings 10 may be arranged for observing the arcs 40' and for introducing the'contact material 6. Other openings 11 in the sidewall permit charging of the crucibles and may be used also for removing glass with for instance a blowpipe. To remove the crucibles openings 12 are provided in the sidewall.

T he invention may be applied also to furnaces which are oval or rectangular in cross sectionand which are provided with any number of crucibles. The crucibles, how- One ever, should not be made too deep in view of the fact that the melting of the charge would thereby be rendered difiicul-t. The electrodes may be movable up and down and ma be iven various an ular ad'ustments asdesired. The roof of the furnace may, for several purposes, be made'removable.

In the use of. furnaces constructed in accordance with the present invention the carbon particles which fall from the electrodes during a heating operation do not enter the materials being melted, as isthe case in furnaces of the type wherein the electrodes are located centrally above the charge instead of being arranged adjacent the sidewall of the furnace and to one side of the materials being treated as in the furnaces illustrated in the accompanying drawings. If desired channels may be provided inthe bottom of the furnace for special heating purposes, resistances being located in said channels. If desired electrodes may be used instead of resistance material for this purpose. i

I claim:

1. Inan electric furnace the combination of a plurality of electrodes projecting downward into a heating room toward projections from the side Wall corresponding to each electrode and supporting carbonaceous contact material for arcs from the electrodes.

2. In an electric furnace the combination of a plurality of electrodes projecting downward into a heating room toward projections from the side wall corresponding to each electrode and supporting carbonaceous contact material forarcs from the electrodes and means for changing the connection of the electrodes with the source of power from delta to star coupling.

3. In an electric furnace the combination ofa plurality of electrodes projecting downward into a. heating room toward projections from the side Wall corresponding to each electrode and' supporting carbonaceous contact material for -arcs from the electrodes and a crucible located in the heated space 

